It is common for lawn and garden equipment such as garden tractors or riding lawn mowers to have internal combustion engines with electric ignition systems. The electric ignition systems of garden tractors are usually powered by batteries carried on the equipment. The flow of electricity from the batteries to the ignition systems is often controlled by key-actuated rotary switches like those found on automobiles.
The rotary ignition switches found on garden tractors generally have either three or four switching states. In the "off" state, the engine magneto is grounded and the tractor does not run. The "run" state, as the name implies, is the state in which the tractor does run. In the "start" position, the starter solenoid is active to start the engine running. The lights may be connected to the battery in the "run" state, or a separate "run/lights" state may be provided in which the lights are activated. Other accessories on the tractor, such as the blade clutch in the case of a riding lawn mower, are coupled to the battery by means of separate power take-off switches in series with the rotary ignition switch.
These rotary switches are "turned" to the "off," "run" or "start" state by means of keys which engage shafts inside the housings of the switches. Spring-biased detents are often incorporated into the shafts and housings so that the shafts remain in the "off," "run" or "run/lights" orientations after the operator releases the key. An additional spring is often incorporated to bias the switch away from the "start" state, so that the switch will revert from the "start" state to the "run" or "run/lights" state after the key is released.
Each input or output of the ignition switch, such as the ground, the battery, the engine magneto, the lights and the starter solenoid, is assigned to a separate switch terminal. The layouts of such ignition circuits vary from manufacturer to manufacturer and from model to model. Consequently, a single parts supplier may be called upon to provide a variety of rotary switches having the same housing but different terminal assignments or different combinations of terminals bridged in the "off," "run," "run/lights" or "start" states.
U.S. Pat. No. 3,497,644 to Schink et al. proposed rotary switch for controlling a garden tractor ignition circuit which included a terminal board mounting a number of active and dummy terminal points in a circle around a central axis. An hour-glass shaped contact was rotatable about that axis and bridges exactly three of the active or dummy terminal points in "off," "run" and "start" angular orientations. Outwardly-extending prongs arranged for connection with the external inputs and outputs were fabricated with integral straps which ran along the lower surface of the terminal board to connect the terminal points with prongs. Additional straps were provided on the upper or lower surface of the terminal board to couple active terminal points where the same terminal prong was to be active in more than one orientation of the contact. In order to change the assignment of the terminals, it was necessary to use a different set of straps and prongs connecting different prongs with different terminal points.
As a general rule, the parts supplier must be able to ship large quantities of switches in a short time to meet the manufacturing schedules of the lawn and garden manufacturer. This requires the parts supplier to maintain an inventory of switches or switch components which can be assembled and shipped on short notice. The inventory which the parts supplier must maintain in order to meet short deadline orders is exacerbated by the need to maintain different styles of terminals, terminal plates and straps in order to meet the needs of different manufacturers and models of equipment.